[R6RS] shall versus must

[dyb at cs.indiana.edu]

I caught only the tail end of the "shall" versus "must" dicussion as I
came on the line Tuesday (I think).  Can someone explain the rationale
behind the universal change?  I seems more natural to me to use "must" for
syntactic or input requirements, as in

  \hyper{Formals} must be a formal arguments list as described below

and "shall" for things like requirements on return values:

  the value returned by {\cf eqv?} shall be a boolean

Kent